Tolerance intervals are a range of values for a specific quality characteristic of a product that likely covers a specified minimum percentage of current or future product output. Use Tolerance Intervals (Normal Distribution) to determine the range within which a specified proportion of the process measurements is expected to fall when your data come from a normal distribution.
For example, a parts manufacturer wants to evaluate the variability of the width of a part. Technicians randomly sample 30 parts and measure the width in millimeters (mm). The manufacturer uses a two-sided tolerance interval to determine the range within which the widths of parts are expected to fall. If this range is wider than the requirements, the process might manufacture excessive waste.
To perform a tolerance interval analysis, choose .
If you want to calculate tolerance intervals when your data do not come from a normal distribution, use nonnormal tolerance intervals.